Subaru Impreza Head Seal Replacement
My girlfriend just approached her 80,000 miles of operation on her 2007 Subaru
Impreza, and during the maintenance that I perform on her car, I decided to take
a look at the condition of her spark plugs. When I removed the passenger side
ignition boot, I noticed that there was oil leaking into the spark plug galley.
After doing some research, I found that this is a common issue that every Subaru
owner will face during the course of ownership. The cause was a failed head seal
and spark plug seal.
This project is pretty extensive, and in turn, requires a significant amount of
tools to make the job easier.
It is VERY important that you get yourself a universal joint to do this task. DO NOT
start without one unless you have super midget hands and can get in tight areas.
First things first is to make as much room as you can to work. If you have a newer non-turbo Impreza,
chances are you have a SOHC model which means that the head covers are going to be a bit
tough to get to. I personally removed the hood, but I wouldn't recommend this unless you know how to
throw it back on ... it can be quite cumbersome if you have trouble aligning the bolts and could end
up damaging the hood.
I am not going to go into the details of how to remove the intake and the battery, these can be found
all over the web, but ultimately this is something you want to do to make room to work. Here is the
area without the intake...
And the driver side sans battery...
What you want to do here is disconnect any wires that are directly connected to the valve head, which
on this engine is the spark plug boots. Start by disconnecting the spark plug wires from the distributor.
If you are unsure where this is, simply follow the spark plug wire towards the back of the engine. The
distributor is found on the passenger side.
And next, remove the spark plug boots from the head itself. They will pull right out, and if you have
done a spark plug change before, they shouldn't be on there with too much grip. Another thing that you
want to remove is the intake breather hose. This uses a simple pinch clamp, and the other end is connected
the same way under the intake resonator box.
Take note of the highlights in the image below. These are 10mm bolts and there are 6 per side.
Take note that these bolts have seen their share of heat cycling during their
lifetime. You should surely spray some WD40 or PBBlaster on them just to help them break free.
These bolts aren't torqued down very hard, and can easily be removed with a box end wrench ...
DO NOT put extreme force on these bolts, if they break, you are going to be
in deep doo doo.
If you are following this tutorial correctly, and you are on the passenger side, there is one more
bolt that you need to worry about, and that is on the timing belt cover.
This is where the universal joint and some extensions will come in very handy. I took it one step
further and used an impact driver. Again, I dont recommend this unless you have used an impact
driver with a joint before. If you arent careful, you can lose control of the joint and cause some
serious damage.
Take note of the one shorter bolt on the passenger side, remember that this goes where the timing
belt cover is.
I noticed that a few guides online don't really mention this step, but it will make the job a heck of
a lot easier. There are a total of 4 12mm bolts, and 2 10mm bolts.
The yellow colored circles are the 12mm bolts, with the solid yellow indicating the location of two
hidden bolts. The red circles are the 10mm bolts. Once you undo these, the shield easily slides
off.
Undoing the bolts isn't simply going to make the head cover come off. You will need to work a bit
to break the seal created by the rubber gasket. This can be easily done by grabbing a long flat head
screwdriver and giving it a few light taps with a hammer.
The head cover is going to gently start sliding off, and this is where the "hard" part comes, which is trying
to remove the head cover with the limited room you have. It is most certainly possible, and possible without
any excessive force. Excessive force may damage the internals of the engine, please be VERY careful
here. I eventually got the cover out by working the cover towards the back of the engine, and then
up through the engine bay. Take your time, and eventually you will get it.
Once the cover is off, check for each of the gaskets. There should be one large gasket that is either going to
be stuck to the cover, or stuck in place on the engine. You can see from the picture above that the gasket
is right on the engine. The large 'tubes' in the center of the head are the spark plug galleys. There
are two gaskets around them as well, in my case they were actually stuck on the cover.
You will immediately see the difference between your new spark plug gaskets and the old ones.
The image below shows the older work seals on the left with the new seals on the right.
Give the spark plug galleys and clean with a shop towel to get the oil off, then press on the
new seals. They only go on one way, and you need to make sure they are pressed on fully and
seated evenly.
Take some time to clean the cover. Chances are there is a lifetime of oil gunk and grime that has
coated the cover, and you really want to make sure that it is nice and clean. You also want to
make sure that the valley for the gasket is free of oil and clean of any dirt an debris. Use some
carb cleaner, and dry well.
The head gasket goes on only one way, and the easiest way to figure it out is to find the curve
on the gasket to match it with the curve on the head. Make sure the seal is nice an clean, and that
it is installed fully.
Once this is done, go ahead and work on getting the head cover back on the engine. Again, be very
careful here, and take your time. It will go back on without any excessive force. Reinstall the head
cover bolts using a ratchet. To not use power tools here, you want to make them tight, but not excessive
as you may damage the gasket.
The driver side is going to be slightly easier as there is a bit more room to work with, but the
concept is exactly the same. There are a few extra things that you will need to worry about though
The first difference is the layout of the fuel rail shield. Above you will see a picture that I took
that hopefully shows you where all of the bolts are. These are all 12mm bolts.
Another thing you will want to remove here to make the job easier is the oil fill tube. This goes
directly to the head cover and is attached by two 10mm bolts.
Once you reinstall everything, and make sure that all lines have been reconnected, you really should prime
the engine. Chances are when you removed the head covers, a large amount of oil spilled on the ground,
which is perfectly fine. First, you want to go and add about a half quart of oil to replace what spilled out.
What you want to do though, is have engine oil back into the heads to coat the parts.
It is very easy to do this just by removing the ignition fuse in the fuse panel under the steering wheel. Once
you do this, turn the ignition for about 3 seconds ... wait .... and again for 3 seconds. Now replace the fuse.
This simply primed the oil pump without starting the engine.
Now go ahead and start up the engine. If all goes well, your engine should turn over fine (might take a bit of
cranking since you had the battery disconnected). Quickly check the head covers, and make sure there are no leaks
and no strange noises. Let the engine idle for a bit if you can (it may stall out, again, this is because of the
battery disconnect). After the engine has warmed up, take it for a quick, gentle drive. When you return, check again
for leaks. No leaks means you did the job right! :)
Lastly, you will want to go ahead and do a full oil change. There is a chance that you contaminated the oil while
doing this, and it is always best to have some nice fresh oil in the car after doing some work.
Subaru Impreza Head Seal Replacement
Requirements
Getting Started...
Dismantling The Head (Passenger Side)
Removing The Fuel Rail Shield
Popping Off The Head Cover
Replacing The Gaskets
Off To The Driver Side
Done? ... Almost